GCN Circular 2081

A. Zeh, S. Klose (Thueringer Landessternwarte Tautenburg),
J. Greiner (MPE Garching),

report:


Using the light curves of SN 1998bw (Galama et al. 1998, Nature 395,
670) as a template we have analyzed what color changes are expected to
be seen in the optical transient following GRB 030329 if a supernova
component would appear.


Ingredients:
------------

1) SN 1998bw:

- A_V = 0.20 mag (Woosley, Eastman, & Schmidt 1999, ApJ 516, 792)
- no time delay between the onset of the SN and the onset of the GRB
- A_V(host) = 0.0 mag


2) The host galaxy:

- z = 0.1685 (Greiner et al. 2003, GCN 2020
Not found
 
 
)
- a negligible host flux in BVRI (based on R>22.5; Blake & Bloom 2003,
  GCN 2011
Not found
 
 
)
- A_V(Galaxy) at (l, b) = 217.07, b = 60.68:
  E(B-V) = 0.025 (Schlegel, Finkbeiner, & Davis 1998, ApJ 500, 525),
- R_V = 3.1


3) The GRB afterglow:

- Considering published GCN R-band data, analyzed according to
  Beuermann et al. (1999, A&A 352, L26), we find:

  alpha_1 = 0.85 +/- 0.04
  alpha_2 = 1.55 +/- 0.02
  t_break = 0.42 +/- 0.03 days,

  after ignoring the several re-brightenings during the last days

- colors (best fit):
  B-V = 0.39 mag
  V-R = 0.34 mag
  R-I = 0.47 mag

- we have taken into account the latest re-brightening episode and assumed that
  a) alpha_2 remains constant and b) the color of the afterglow does not change


Output cocktail:
----------------

 - Fig. 1: the light curve
 - Fig. 2: the expected color evolution

We note that differences in the reported value for alpha_2 (cf. Li
et al. 2003, GCN 2078
Not found
 
 
) can be explained by slightly different
selection criteria for the data chosen to perform the numerical fit.

http://www.tls-tautenburg.de/research/klose/grb.html


Warning:
--------

These results are based on a simple toy model. They provide only a
hint about what the strength of the SN signal could be since most
SN bumps found so far had a brightness of only 30-80% of SN 1998bw.